Thorax 3 - Mediastinum Flashcards by Urvi Bihani

What separates mediastinum into superior + inferior

T4/5 horizontal line

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Mediastinum is divided into:

Superior mediastinum - superior thoracic aperture
Inferior Mediastinum - inferior thoracic aperture. It’s further divided into: anterior (sternum + pericardium), middle (pericadium + heart), posterior (pericardium + thoracic vertebrae)

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Mediastinum contents (THOT GN)

Trachea
Heart + pericardium
Oesophagus
Thoracic duct 
Great vessels
Nerves

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Where does apex of heart lie

5th IC space in MCL

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Great Veins passage

Internal jugular veins (head) + subclavian veins (upper limbs) form brachiocephalic veins. R+L brachiocephalic veins = SVC w drains into RA

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Superior mediastinum (anterior to posterior)

Thymus behind sternum
Phrenic nerves
Great veins
Main lymphatic trunks
Vagus nerve 
Great arteries
Trachea + main bronchi
Upper oesophagus

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Superior mediastinum - Azygous vein

drains posterior chest wall, upper abdomen + posterior mediastinum
Arches over R lung root and drains into SVC
Accessory Hemiazygous veins on L cross thoracic vertebral bodies to join azygous vein on RHS

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Superior mediastinum - Arteries (4)

Aorta: ascending, arch, descending
Common carotid
Coronary artery
pulmonary trunk

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Superior mediastinum - common carotid

divides into external + internal carotids high in neck. Main arteries of head and neck

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Superior mediastinum - coronary artery

L coronary artery arises from L aortic sinus

R coronary artery arises from R aortic sinus

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Superior mediastinum - pulmonary trunk

divides into R + L pulonary arteries.

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What connects pulmonary trunk to descending aorta

ligamentum arteriosum (remenant of ductus arteriosus as blood bypassed lungs in foetal life)

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Vagus nerves

Lateral to common carotid.

L vagus passes anterior to aortic arch, crosses behind lung root and gives L recurrent laryngeal nerve w branches in oesophagus

R vagus lies on trachea, crosses posterior to lung root and = R recurrent laryngeal nerve.

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Phrenic nerves are ___ of lung root

Vagus nerves are ____ of lung root

Phrenic = anterior
Vagus = posterior

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Middle Mediastinum contents

Pericardium
Heart
Great vessel origin
Nerves

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Pericardium (superior and inferior parts)

Inferiorly, continuous and blends w diaphragmatic central tendon
Superiorly, continuous and blends with outer layer of great vessels in superior mediastinum

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Pericardium has 2 layers

Fibrous - tough connective tissue outlines middle mediastinum boundaries. Blends w great vessels in superior mediastinum

Serous - has some fluid in it = movement of heart. Has parietal + visceral parts. Visceral adheres to heart and forms its outer covering. Parietal lines inner surfaces of fibrous pericardium

Parietal layer cont w visceral layer @2 reflections = oblique pericardial sinus posteriorly + transverse pericardial sinus

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Pericardial attachments

base - central tendon of diaphragm

anteriorly attached to sternum by sternopericardial ligaments

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innervation of fibrous pericardium

phrenic nerves

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Pericardial sinus

Transverse + Oblique

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Transverse pericardial sinus

separates arteries + veins.
posterior to aorta + pulmonary trunk
anterior to SVC + veins

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Oblique pericardial sinus

formed by reflection onto pulmonary veins of heart

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Pericardial effusion

build up of excess fluid in pericardial cavity. Bc firbous pericardium is fixed, can’t expand v easily = increased pressure compresses heart (cardiac tamponade) = biventricular failure

Pericarditis

inflammation of pericardial layers - common cause of chest pain + can lead to cardiac tamponade

Branches of aortic arch

braciocephalic, L common carotid, L subclavian Brachiocephalic goes to change

Heart surfaces

Apex: formed by inferolateral part of LV Base: LA, some RA, proximal parts of great veins. Sides:diaphragmatic surface, R pulmonary (RA)), L pulmonary(LA + LV), anterior sternocostal surface (contains RV, some RA + LV)

Valves

tricuspid (RA + RV): 3 cusps mitral (LA + LV): 2 cusps pulmonic (RV + Pulm): 3 cusps aortic (LV + Aorta): 3 cusps

Septa separating heart chambers

interatrial interventricular atrioventricular

R coronary artery supplies

RA, RV, SAN, AVN, posteriorinferior 1/3rd of interventricular septum and some of posterior LV

R coronary main branches

SAN artery R marginal artery Posterior descending

L coronary artery supplies

LA, LV, atrioventricular branches and bundles

L coronary artery main branches

circumflex artery - lateral supply, mainly LA and LV | Left anterior descending (LAD) - anterior supply

Dominance of arteries

R dominant: if SAN + posterior descending comes from R coronary artery L dominant if SAN + Posterior descending comes from L circumflex artery

Cardiac veins (4)

``` Great cardiac Middle cardiac Small cardiac Posterior cardiac drain into coronary sinus w empties into RA by opening of IVC ```

Cardiac arrest vs MI

cardiac arrest - lack of heart beat generation | MI: heart muscle death bc of blockage

Cardiac sympathetic innervation

T1-5 sympathetic nerves

Dorsal root and ventral root

dorsal - where somatic/autonomic neurons enter | ventral - where they emerge

IC somatic nerves

Arise from anterior rami of spinal nerves T1-11 as mixed nerves w form lateral cutaneous branches These split into anterior + posterior branches innervating skin. End as lateral + medial branches w form anterior cutaneous branches

Phrenic somatic nerves

anterior rami of spinal nerves C3-5 w combine to form 2 phrenic nerves - L = over aortic arch - R = lateral to SVC

Autonomic visceral inenrvation

PS - C3,7,9,10 and S2-4 | S - T1-L2 (sympathetic outflow from spinal cord)

Sympathetic outflow from spinal cord

outflow originates lateral horns of spinal cord T1-L2 Preganglionic neurons exit via ventral horm Enters sympathetic ganglion through white rami communicans Synapse w postganglionic fibres in gnaglion and leave via grey rami communicans postganglionic neuron then joins onto spinal nerve to go to target organ

sympathetic nerves to lungs and heart

mainly T2-4

PS outflow (5 nerves)

``` Oculomotor (CN3) Facial (CN7) Glossopharyngeal (CN9) Vagus (CN10) Sacral (S2-4) ```

Vagus Nerves

arise from medulla, leave skull through jugular foramina. .descend neck postolateral to common carotid artery Both vagus nerves form plexus around oesophagus R + L recurrent laryngeal nerves are branches

Pulmonary plexus

PS nerves constrict bronchioles S nerves dilate bronchioles mix of S + PS nerves

Cardiac plexus

sympathetic efferents increase HR and contraction force | PS efferents decrease HR

Oesophageal Plexus:

S: pain sensation | part of ENS

Which chamber of heart is pectinate muscle most numerous

RA - pectinate muscles fan out from crista and found in R auricle

Trabeculae carnae (papillary muscles) are coarser/rougher in which chamber of heart

3 types of papillary muscle in RV

Anterior Posterior Septal

most areas supplied w R coronary artery is drained by 2 cardiac veins:

Middle + small (R cardiac) veins

The vessel draining the posterior wall of the thorax and abdomen, arching over the right lung root and draining into the SVC

Azygous veins

Formed by the asymmetric union of right and left brachiocephalic veins

SVC

Superior mediastinal structure almost non-existent in the elderly due to atrophy

Thymus

Lymph nodes associated with the internal thoracic arteries

Parasternal nodes